The disclosure of Japanese Patent Application No. HEI 11-67502 filed on Mar. 12, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a structure for coupling two types of members that are different in coefficient of thermal expansion.
2. Description of the Related Art
For example, as a related art, a coupling structure between an air hose for supplying air to a vehicular engine and a resonator for reducing column resonance is known.
FIG. 5 is an exploded perspective view of an air hose and a resonator, FIG. 6 is a plan view of the air hose and the resonator, and FIG. 7 is a sectional view of the air hose and the resonator in FIG. 6 taken along line VIIxe2x80x94VII. As shown in FIGS. 5 through 7, a portion of an air hose 101 is fit into a concave portion 102a of a resonator 102, and a cylindrical opening 101a of the air hose 101 is fit into a cylindrical hole 102b of the resonator 102. An annular joining member 103 is disposed between the cylindrical opening 101a and the cylindrical hole 102b, and the annular joining member 103 is embedded in an outer peripheral wall of the cylindrical opening 101a and in an inner peripheral wall of the cylindrical hole 102b so as to reinforce the coupling between the two members 101 and 102 and to provide sealing between the two members 101 and 102.
FIG. 8 is an enlarged sectional view of the annular joining member 103 disposed between the cylindrical opening 101a and the cylindrical hole 102b. The cylindrical opening 101a and the cylindrical hole 102b are engaged with each other at portions S1 and S2, respectively. The annular joining member 103 is shaped like a hook, and is embedded in the outer peripheral wall of the cylindrical opening 101a and in the inner peripheral wall of the cylindrical hole 102b. 
The air hose 101 (shown in FIGS. 5 through 8) is disposed inside an engine room of a vehicle in a freely bendable manner. Therefore, material of the air hose 101 must have sufficient elasticity, and such material as polypropylene (PP), for example, is used. On the other hand, in many cases, the resonator 102 is disposed near an engine inside the engine room of the vehicle. Therefore, the resonator 102 requires a heat-resistant material such as nylon (PA).
Further, because chemical bonding of polypropylene and nylon is difficult, the annular joining member 103 is used to enhance sealability. Modified polypropylene, for example, is used as a material for the annular joining member 103.
However, the coefficient of thermal expansion for polypropylene is between 5xc3x9710xe2x88x925Kxe2x88x921 and 11xc3x9710xe2x88x925Kxe2x88x921, and between 2xc3x9710xe2x88x925Kxe2x88x921 and 3xc3x9710xe2x88x925Kxe2x88x921 for nylon, and there is a difference in coefficient of thermal expansion between the two materials. Also, a significant temperature fluctuation is caused in the vehicle engine room. Each time a significant temperature change is repeated, mismatch occurs between the cylindrical opening 101a of the air hose 101 and the cylindrical hole 102b of the resonator 102, due to the difference in coefficients of thermal expansion of polypropylene and nylon. Because the cylindrical opening 101a and the cylindrical hole 102b are engaged with each other at the portions S1 and S2, respectively, the mismatch between the cylindrical opening 101a and the cylindrical hole 102b cannot be counterbalanced. Consequently, a stress caused by the mismatch acts on the annular joining member 103, which may lead to breakage of the annular joining member 103.
Also, it is preferable that the annular joining member 103 be made compact and light-weight, because modified polypropylene used for annular joining member 103 is expensive. Making the annular joining member 103 larger for the improvement of strength leads to cost increase.
It is an object of the present invention to provide a structure for coupling two types of members which is capable of preventing breakage of a joining member used for joining two types of members having different coefficients of thermal expansion.
In a first aspect of the present invention, the walls of a first member and a second member that are different in coefficient of thermal expansion are superposed, and a joining member is embedded in respective walls of the first member and the second member to couple the two types of members, the first member and the second member. In this coupling structure, in a peripheral range of the joining member, a concave portion is formed in the wall of the first member, and a convex portion is formed on the wall of the second member. The concave and convex portions fit with each other.
According to the above aspect, the concave and convex portions of the first and the second members are fit in the peripheral range of the joining member. Accordingly, even if mismatch occurs between the first member and the second member due to the difference between coefficients of thermal expansion of the first and the second members, a stress generated thereby is received by a fitting section of the concave and the convex portions. Therefore, the stress does not entirely act on the joining member. Thus, the breakage of the joining member is prevented.
Further, in the above-mentioned aspect, the coefficients of thermal expansion of the first and the second members are different, and the concave portion is formed in either the first member or the second member having larger coefficient of thermal expansion than the other.
For example, if the coefficient of thermal expansion of the first member is greater than that of the second member, a convex portion is formed in the second member in advance. The temperature of the first member is raised up to its melting temperature, and then the first member is pressed against the second member. Thus, a concave portion to be fitted with the convex portion on the second member is formed in the first member. Because the coefficient of thermal expansion of the first member is the larger, the concave portion of the first member shrinks more than the convex portion of the second member when the first member is cooled down to a room temperature range. Accordingly, a clearance is not formed between the concave and convex portions, and the effect obtained from fitting the aforementioned concave and convex portions is maintained.